ESTRO 2025 - Abstract Book

S3886

Radiobiology - Immuno-radiobiology

ESTRO 2025

3816

Proffered Paper Radiation activates the AIM2 inflammasome to enhance immunotherapy by triggering IL-1β signaling and DC activation in colorectal cancer Shujuan Zhou 1 , Peiyuan Mu 2 , Qianyu Zhou 2 , Lijun Shen 1 , Yan Wang 1 , Hui Zhang 1 , Juefeng Wan 1 , Zhen Zhang 1 , Fan Xia 1 1 Department of Radiation Oncology, Fudan University Shanghai Cancer Center, Shanghai, China. 2 Department of Oncology, Fudan University, Shanghai, China Purpose/Objective: Microsatellite stable (MSS) colorectal cancer (CRC) responds poorly to PD-1 blockade monotherapy but can benefit from its combination with radiotherapy. Radiation induces antitumor immunity through multiple cytosolic nucleic acid sensing pathways. However, the role of the DNA-sensing absent in the melanoma 2 (AIM2) inflammasome and its downstream IL-1β remains unclear. This study aims to investigate the function of the AIM2 inflammasome in combined radiotherapy and immunotherapy and to explore the underlying mechanisms. Material/Methods: Two CT26 cell lines with distinct sensitivities to combined therapy were generated, by in vivo passaging for four cycles in BALB/c mice treated with 8Gy×3Fx radiation and PD-1 antibody. One cell line was sensitive, and the other resistant. Bulk RNA-seq, WB, and IHC were performed on sensitive and resistant CT26 to investigate the correlation between the AIM2-IL-1β pathway and the response to combined therapy. Flow cytometry and lentivirus-mediated shRNA targeting AIM2 were used to assess the impact of IL-1β on DC function. AIM2 expression in tumor samples was examined using scRNA-seq data from a clinical trial in which patients with locally advanced MSS rectal cancer underwent neoadjuvant chemoradiotherapy and PD-1 blockade.

Results:

RNA-seq revealed higher expression of AIM2 and a preferential enrichment of cytosolic DNA-sensing pathway in treatment-sensitive tumor cells. CIBERSORT analysis further showed that the expression level of AIM2 was positively correlated with the abundance of tumor-infiltrating immune cells including CD8+ T cells (total, Tcm, and Tem), non regulatory CD4+T cells, memory CD4+T cells, and activated DCs. Similar correlations were observed in colorectal samples from the TCGA database. Higher levels of AIM2 localized primarily to the nucleus of treatment-sensitive tumor cells were confirmed using WB and IHC. Importantly, 24h after 8Gy radiation, AIM2 was recruited to and densely concentrated within cytosolic micronuclei clusters resulting from nuclear damage in treatment-sensitive tumor cells. The AIM2 inflammasome was then activated evidenced by increased levels of cleaved caspase-1 and IL-